Hi Corby, best advice is don't use EE

I'm losing patience with it now. To answer your question, I did get it working temporarily, but then enabled CAPTCHA out of curiosity. Didn't work, so I tried disabling it, but it's stuck enabled. Turns out it's a bug in my version of EE (2.53) and Safecracker.
But you can't update Safecracker without updating EE now that Ellis have acquired Safecracker and integrated it by default. And the EE site has changed so I can no longer download up-to-date files without paying again. Can try and edit the DB directly (absolute mess in there for plugin settings - using serialised JSON) but it still seems to be enabled elsewhere.
The solution I used anyway was fairly complicated (to me at least) and took quite a bit of fiddling to get it working, but it's a combination of Matrix (a plugin you'll need to pay for) and Safecracker (bundled as standard in recent EE versions). If you decide to try that, I'd be happy to post my template and tell you what options I have set in the back-end. Can't recall the steps I took to set it up though unfortunately.